Field of the Invention
Embodiments of the present invention relate to electrical overcurrent protection devices, and in particular to electronic trip units for circuit breakers.
Description of Related Art
Circuit breakers are used in electrical distribution systems to protect electrical conductors and equipment against the effects of short circuits, ground faults, overloads and/or overcurrent conditions (collectively “abnormal current conditions”). Some circuit breakers have programmable electronic controllers for controlling operations of the circuit breaker. The programmable electronic controllers are known as electronic trip units and circuit breakers employing electronic trip units are known as electronic trip circuit breakers. The electronic trip unit monitors the conditions of an electrical circuit protected by its associated circuit breaker, and signals the circuit breaker to trip upon detecting an abnormal current condition. Current transformers (CTs) are often employed on the conductors of the circuit protected by the circuit breaker to provide a current level signal to the electronic trip unit. Current transformers have a polarity, and it is possible to improperly install a current transformer in the electrical circuit. For example, the CT could be installed backward on a phase conductor of the electrical circuit, or the secondary conductors from the CT could be connected to the electronic trip unit with reversed polarity. In either scenario, the CT will be connected to the electronic trip unit with an improper polarity. Installing CTs with an improper polarity can result in nuisance ground fault tripping until the improperly installed CTs are discovered and corrected.